Goals: The Advanced Composition Explorer's prime objective is to measure and compare the composition of particles that travel to us from the Sun, the space surrounding our solar system, and elsewhere in the Galaxy. The mission also seeks to advance our ability to forecast space weather in the coming years when humans will venture beyond Earth's protective magnetosphere.

Accomplishments: ACE continues to provide space weather reports and warnings of geomagnetic storms that can disrupt communications on Earth and harm astronauts in space. The spacecraft has operated far beyond its expected lifetime.